1. Field of the Invention
The present invention relates to an automatic transmission control apparatus, which controls engagement and disengagement of each corresponding one of a plurality of friction arrangements of an automatic transmission of a vehicle by controlling application of a fluid pressure of operating fluid to a corresponding one of a plurality of drive pistons, which are assigned to and drive the plurality of friction arrangements, respectively.
2. Description of Related Art
In the automatic transmission control apparatus of the above type that controls the fluid pressure, a piston chamber, which applies the fluid pressure to the drive piston assigned to the corresponding friction arrangement (e.g., a clutch or a brake), is emptied in a disengaged state of the friction arrangement. In this state, when gear shift, which causes the engagement of the friction arrangement, needs to be performed, the operating fluid is supplied in the piston chamber to stroke, i.e., slide the piston. However, in this instance, the piston cannot be slid until the working fluid is filled in the piston chamber. Therefore, the engagement of the friction arrangement disadvantageously requires a relatively long period of time. In order to address the above disadvantage, a rate of increase in the applied fluid pressure per unit time may be increased to shorten the time required for achieving the engagement of the friction arrangement. However, in such a case, a gear shift shock is increased to cause deterioration in the gear shift feeling of an occupant of the vehicle.
Japanese Unexamined Patent Publication No. H05-296327 addresses the above disadvantage by providing a control apparatus that applies an oil pressure to the clutch in a very little level that does not cause the slide movement of the piston before the gear shift takes place. That is, in this control apparatus, the piston chamber can be filled with the operating oil before the next gear shift takes place. Thus, the time required for the engagement of the clutch can be shortened without rapidly increasing the oil pressure applied to the piston.
However, in the control apparatus of Japanese Unexamined Patent Publication No. H05-296327, the oil pressure, which is applied to the piston before the next gear shift, is made relatively small level that does not cause the slide movement of the piston. Thus, there is still required substantial time between the initiation of the actual gear shift and implementation of torque transmission upon engagement of the clutch due to the required substantial slide movement of the piston. Thus, there is the limitation on the shortening of the time required for the engagement and thereby on the shortening of the gear shift. As a result, a recent market demand of achieving high gear shift response cannot be met, and thereby the good gear shift feeling of the occupant cannot be made.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide an automatic transmission control apparatus, which provides improved gear shift feeling.
To achieve the objective of the present invention, there is provided an automatic transmission control apparatus, which controls engagement and disengagement of each corresponding one of a plurality of friction arrangements of an automatic transmission of a vehicle by controlling application of a fluid pressure of operating fluid to a corresponding one of a plurality of drive pistons, which are assigned to and drive the plurality of friction arrangements, respectively. The automatic transmission control apparatus includes a selecting means and an applying means. The selecting means is for selecting each corresponding one of the plurality of friction arrangements, which is driven in an engaging direction to achieve the engagement at time of next gear shift to transmit torque, as a standby friction arrangement that is placed in a standby state for implementing the next gear shift. The applying means is for applying a standby fluid pressure to each corresponding one of the plurality of drive pistons, which drives the corresponding standby friction arrangement, before the next gear shift. The standby fluid pressure is for sliding each corresponding one of the plurality of drive pistons, which drives the corresponding standby friction arrangement, within a range that does not cause transmission of the torque through the corresponding standby friction arrangement.